1. Field of the Invention
The present invention relates to a system and method for controlling engine revolutions for a hybrid construction machine. More particularly, the present invention relates to a system and method for controlling engine revolutions for a hybrid construction machine, which can prevent the occurrence of engine revolution drop in a hybrid construction machine.
2. Description of the Prior Art
In general, a construction machine such as an excavator in the related art has a hydraulic driving system which drives a hydraulic pump by a fuel engine and drives an actuator by hydraulic pressure.
FIG. 1 is a necessary torque output relationship diagram of an excavator system in the related art. As illustrated in FIG. 1, in a hydraulic excavator in the related art, an opening area of a main control valve (MCV) 7 is adjusted in accordance with an output of a pilot valve 6 through a user's manipulation of a lever 5. Hydraulic fluid discharged from a hydraulic pump 13 is transferred to respective hydraulic systems with its flow rate adjusted in accordance with the opening area of the MCV 7. Since the driving of the hydraulic pump 13 is performed by a fuel engine 10, the efficiency thereof is relatively low.
In the construction machine such as the hydraulic excavator in the related art, it is sometimes required to perform working as greatly changing an engine output so as to cope with great load change, and it is required to seek improvement of mileage by effectively utilizing the engine output. Accordingly, a hybrid technology using an electric motor-generator that is adopted in a hybrid vehicle has been planned to be applied to an excavator. That is, a hybrid construction machine, such as a hybrid excavator, in which an engine is connected to an electric motor-generator, has been proposed. According to the hybrid construction machine, in the case of performing a light-load operation, the motor-generator is operated to generate power to charge a battery using a portion of the engine output, while in the case of performing a heavy-load operation, electric energy is provided from the battery to supplement the engine.
An electric motor-generator is attached to the engine of the hybrid excavator. If this electric motor-generator is abruptly operated, engine revolutions (i.e. revolutions per minute (RPM)) may be lowered to cause the occurrence of an engine revolution (RPM) drop. Although the engine returns to its original revolutions by a self-control system, the working performance is lowered in this process.
Also, the lowering of the engine revolution occurs when the load is greatly changed, for example, the load is abruptly increased, during operation of the construction machine.